Brief Description of the Prior Art
A number of types of synthetic resin electrical outlet boxes have heretofore been marketed. A number of these are the subject of United States patents which have previously issued.
In synthetic resin electrical outlet boxes, such boxes are adapted to be secured to the material of construction of a building wall and to provide a junction and/or switching connection by which electrical service may be conducted from the box to certain appliances, lights or other electrically operated devices. Such boxes conventionally have a plurality of electrical leads extended to the box, passed through the wall or the back of the box and secured to terminals within the box. Such boxes also have a removable cover or face plate which is secured to the open front side of the box after the electrical connections have been appropriately made within the box, and prior to placing the box in service.
It is typical in the construction of such synthetic resin electrical outlet boxes to provide one or more knockout panels, windows or plugs in the walls of the box in order to make openings at the location where electrical leads or conduits are to be extended into and connected within the box. Various ways of configuring and making such knockout plugs or windows have been heretofore proposed, but generally, such plugs or windows constitute panels or discs held within the box wall at a certain location thereon by small tabs or hinges which are frangible and easily broken under pressure. One problem which has characterized such knockout panels, plugs or windows has been the rough or asymmetrical defining boundary which surrounds the opening formed when such plugs or panels are removed. This makes it difficult to use connector fittings inserted into or attached to such openings where such connector fittings are to be used to connect a hollow conduit or raceway to the box for the purpose of conveying electrical conductors thereto.
Patented examples of synthetic resin electrical outlet boxes of the type described are the boxes which are illustrated in the following U.S. and foreign patents:
______________________________________ U.S. PATENTS 2,867,349 Parker 4,105,862 Hoehn 3,876,821 Pringle 4,248,459 Pate el al 4,315,100 Haslbeck et al 4,306,109 Nattel 4,071,159 Robinson et al 4,036,389 Pate el al 2,804,116 Van Niel et al 3,575,313 Trachtenberg Re 28,489 Schindler et al 4,215,787 Moran et al 3,895,732 Robinson et al 4,167,648 Lockwood 2,299,696 Gregersen 3,863,037 Schindler et al 3,863,021 Schindler et al 3,740,451 Schindler et al 3,353,701 Palmer 4,130,335 Kinney 4,281,773 Mengue FOREIGN PATENTS Dutch Patent 87,242 British Patent 1,204,338 British Patent 811,544 West German 1,036,974 ______________________________________